As is well known in the art, conventional inkjet printers generally employ one or more inkjet cartridges, often called “pens”, which eject drops of ink onto a page or sheet of print media. The pens are usually mounted on a carriage, which is arranged to scan relative to a sheet of print media as the pens print a series of individual drops of ink on the print media. Often, the pens scan across a scan axis relative to a stationary sheet of print media. The series of drops collectively form a band or “swath” of an image, such as a picture, chart or text. Between scans, the print medium is advanced relative to the scan axis. In this manner, an image may be incrementally printed. In other arrangements, the pens, in the form of a page wide array for example, may remain stationary with the print media being past the print bar.
The distance which an ink drop travels from a print head to the ink receiving surface of the print medium is often known as the pen-to-paper spacing. For high-quality image formation the pen-to-paper spacing is desirably precisely controlled. If the spacing to too little, the risk that a print head may impact against the print media increases. This is especially likely where the print media expands on absorbing water contained in the ink printed on its surface. This expansion may cause undulations or wrinkles in the plane of the print media. As a consequence, the distance between the print media and the print head decreases at some localized points. If, on the other hand, the pen-to-paper spacing is too great, the ejected dots may not be accurately positioned on the surface of the print medium. Other artefacts which also degrade print quality may also occur.
The pen-to-paper spacing in an inkjet printer is set during assembly of the printer. This process is generally repeated only when the carriage is replaced in a major servicing operation.